Glucose sensors of the type employing enzymes are well known. Many of these feature an "enzyme electrode" which consists of an immobilized enzyme such as glucose oxidase that catalyzes a chemical reaction involving glucose and oxygen--a reaction that involves the catalytic conversion of glucose to gluconic acid and hydrogen peroxide with simultaneous consumption of oxygen. The resulting decrease in consumption of oxygen may be measured by a current sensitive oxygen electrode. The production of hydrogen peroxide can also produce a current to be measured by a hydrogen peroxide electrode. Various arrangements for glucose sensors are described in the following U.S. Patents: U.S. Pat. No. 4,703,756 which utilizes first and second tandem sensor elements mounted in a catheter, one of which sensors acts as a reference and the other of which contacts glucose oxidase, whereby an electrical signal is produced indicative of the oxygen content differential between the two sensors; U.S. Pat. No. 4,240,438 which uses a hydrophobic membrane on which the glucose oxidase is immobilized and which senses the rate of oxygen consumption by the glucose contained in the blood; U.S. Pat. No. 4,655,880 which provides a multiple electrode sensor for measurement of glucose concentration by comparing electron current flow in working and counter electrodes in relation to current flow in a reference electrode; U.S. Pat. No. 3,979,274 which utilizes a laminated enzyme electrode with special filtering properties thereby eliminating the need for a compensating or reference electrode; U.S. Pat. No. 4,224,125 which has an enzyme electrode using an oxidoreductase and a redox copolymer acting as an electron mediator in an enzymatic reaction maintained in an immobilized state on an electron collector or semipermeable membrane; U.S. Pat. No. 4,376,689 wherein the coenzyme is immobilized directly on an electron collector (eliminating the need for a membrane) whereby the activity of the enzyme on a substrate can be directly measured; U.S. Pat. No. 4,418,148 employing a contiguous multilayer membrane structure enabling a more homogeneous distribution of enzyme.
At present there does not exist an enzyme type glucose sensor of small enough size to allow insertion directly into blood streams or tissue either directly or via a catheter, which contains a reservoir filled with enzyme immobilized on a powder so as to provide an extended operational lifetime and providing for reuse by refilling.
The inventive miniature glucose sensor can be used to provide continuous monitoring of blood glucose levels in trauma patients suffering from hemorrhagic shock. This will enhance the medical management of such patients in the field, while being transported, and in the hospital, thus increasing survival rates.